1. Field of the Invention
The present invention relates to a compact, small-sized lighting device including at least two lamp units and having a high utilization efficiency of light. The present invention also pertains to a projector-type display apparatus with such a lighting device for producing bright projected images which are uniform in brightness.
2. Discussion of the Background
A lighting device incorporated in projector-type display apparatus generally has a lamp unit, which includes a light source lamp, such as a halogen lamp or a metal halide lamp, and a reflector for reflecting an incident ray emitted from the light source lamp and outputting the reflected ray as a parallel beam or a converging beam in a predetermined direction. Available reflectors have the reflecting surfaces in the shape of paraboloid or ellipsoid.
It is preferable that the lighting device used in the projector-type display apparatus has a large output quantity of light, in order to produce uniform and bright projected images. Further a compact, small-sized lighting device is desirable when being incorporated in portable projector-type display apparatus.
The lighting device may include a plurality of lamp units, for example, two lamp units, in order to increase the output quantity of light. A simple array of the two lamp units in parallel, however, doubles the width of the lighting device and makes the lighting device undesirably bulky. This arrangement also doubles the width of the flux of output light and requires an extended width of the optical path in the lighting device. This further doubles the required width of the optical path formed in the projector-type display apparatus with such a lighting device incorporated therein. This arrangement is thus not suitable for the requirement of the compact, small-sized structure.
A typical example of the lighting device incorporated in the projector-type display apparatus is a lamp unit including a light source lamp having a short arc length and a reflector of a paraboloidal shape having a short focal distance. The distribution of the quantity of light emitted from the lamp unit of this structure is shown as a characteristic curve that has a sharp peak on and in the vicinity of a lamp optical axis and abruptly decreases with a distance from the lamp optical axis. The use of only the light fluxes in a central portion including the lamp optical axis for illumination does not significantly lower the quantity of light.